Immune defects observed in patients with primary malignant brain tumors.

Malignant glioblastomas (gliomas) account for approximately one third of all diagnosed brain tumors. Yet, a decade of research has made little progress in advancing the treatment of these tumors. In part this lack of progress is linked to the challenge of discovering how glial tumors are capable of both modulating host immune function and neutralizing immune-based therapies. Patients with gliomas exhibit a broad suppression of cell-mediated immunity. The impaired cell-mediated immunity observed in patients with gliomas appears to result from immunosuppressive factor(s) secreted by the tumor. This article reviews what has been elucidated about the immune defects of patients harboring glioma and the glioma-derived factors which mediate this immunosuppression. A model involving systemic cytokine dysregulation is presented to suggest how the immune defects arise in these individuals.

Enhanced graft-versus-host disease in older recipient mice following allogeneic bone marrow transplantation.

The incidence and severity of GVHD following bone marrow transplantation increases with recipient age. The role of recipient age on the development of GVHD was analyzed in a semi-allogeneic (C57BL/6-->(C57BL/6 x DBA/2)F1) murine GVHD system. Young adult (2 months) and old (12-14 months) recipient mice were lethally irradiated and reconstituted with young adult T cell-depleted bone marrow (ATBM) or ATBM and young spleen cells. A significantly higher percentage of old vs young recipients developed lethal GVHD. Furthermore, while pre-transplant conditioning with irradiation was not required to observe increased mortality in old recipients, irradiation predisposed the older animals for a more severe course of GVHD, suggesting that GVHD occurred in old compared to young animals in the absence of pre-transplant conditioning but was exacerbated by irradiation. Histologically, the immunological responses in the GVHD target organs were more severe in the old GVHD animals. In support of this observation, increased spontaneous proliferation was observed using lymphoid cells isolated from old vs young GVHD mice. These findings demonstrate that old recipients develop a more severe course of GVHD following BMT, and may present a unique opportunity to study age-related factors in the generation of GVHD.

Apoptotic elimination of peripheral T lymphocytes in patients with primary intracranial tumors.

OBJECT: Patients with gliomas exhibit severe T lymphopenia during the course of the disease. This study was conducted to determine the mechanism(s) responsible for the lymphopenia. METHODS: Using two-color fluorescent staining techniques, the authors show that significant numbers of T cells undergo apoptosis in the peripheral blood of patients with gliomas. To determine whether a glioma-derived factor(s) induces this apoptosis, rosette-purified T cells obtained from healthy donors were treated with glioma cell culture supernatant (GCCS) and examined for apoptosis. It is demonstrated that treatment of normal T cells with GCCS induced apoptosis only with concurrent stimulation of the T-cell receptor/CD3 complex. The addition of neutralizing antibodies to interleukin (IL)-10, IL-4, transforming growth factor alpha, or tumor necrosis factor-beta (lymphotoxin) did not rescue these T cells from apoptosis. Experiments were also conducted in which the degree of monocyte involvement in the induction of T-cell apoptosis was explored. The U937 cells were pretreated for 20 hours with a 1:20 dilution of GCCS. After the removal of GCCS, the U937 cells were cultured in transwell assays with stimulated T cells. Although control U937 cells did not induce apoptosis of the activated T cells, GCCS-pretreated U937 cells induced appreciable apoptosis in normal, stimulated T-cell cultures. CONCLUSIONS: These data indicate that one mechanism by which gliomas cause immunosuppressive effects is the induction of monocytes to release soluble factors that promote activated T-cell apoptosis. The loss of activated T cells leads to T lymphopenia and contributes to the deficiencies in cell-mediated immunity that have been observed during testing of glioma patients' immune function.

Beta1 integrin-mediated T cell adhesion and cell spreading are regulated by calpain.

To investigate the function of calpain in T cells, we sought to determine the role of this protease in cellular events mediated by beta1 integrins. T cell receptor cross-linked or phorbol ester-stimulated T cells binding to immobilized fibronectin induce the translocation of calpain to the cytoskeletal/membrane fraction of these cells. Such translocation of calpain is associated with proteolytic modification of protein tyrosine phosphatase 1B, increased cellular adhesion, and dramatic alterations in cellular morphology. However, affinity-related increases in T cell adhesion induced by the anti-beta1 integrin antibody 8A2 occur in a calpain-independent manner and in the absence of morphological shape changes. Furthermore, calpain undergoes activation in response to either alpha4beta1 or alpha5beta1 integrin binding to fibronectin in appropriately stimulated T cells, and calpain II as well as protein tyrosine phosphatase 1B accumulates at sites of focal contact formation. Inhibition of calpain activity not only inhibits the proteolytic modification of protein tyrosine phosphatase 1B, but also decreases the ability of T cells to adhere to and spread on immobilized fibronectin. Thus, we describe a potential regulatory role for calpain in beta1 integrin-mediated signaling events associated with T cell adhesion and cell spreading on fibronectin.

Human glioma-induced immunosuppression involves soluble factor(s) that alters monocyte cytokine profile and surface markers.

Patients with gliomas exhibit deficient in vitro and in vivo T cell immune activity, and human glioblastoma culture supernatants (GCS) inhibit in vitro T lymphocyte responses. Because APC are essential for initiating and regulating T cell responses, we investigated whether GCS would affect cytokines produced by monocytes and T cells from healthy donors of PBMC. Incubation of PBMC with GCS decreased production of IL-12, IFN-gamma, and TNF-alpha, and increased production of IL-6 and IL-10. The GCS-induced changes in IL-12 and IL-10 occurred in monocytes, and involved changes in IL-12 p40 and IL-10 mRNA expression. Incubation with GCS also resulted in reduced expression of MHC class II and of CD80/86 costimulatory molecules on monocytes. The immunosuppressive effects were not the result of IL-6 or TGF-beta1 that was detected in GCS. However, it was due to a factor(s) that is resistant to pH extremes, differentially susceptible to temperature, susceptible to trypsin, and has a minimum molecular mass of 40 kDa. Our findings show that glioblastoma-generated factors that are known to suppress T cell responses alter the cytokine profiles of monocytic APC that, in turn, inhibit T cell function. This model indicates that monocytes can serve as an intermediate between tumor-generated immune-suppressive factors and the T cell responses that are suppressed in gliomas.